The present invention is generally related to lithographic duplicators and, more particularly, to a versatile system for controlling ink and moisture feed rates during printing.
The production of quality copies by lithographic means requires that the ink and moisture each be supplied at a rate proper for the demands of the lithographic master. It is also necessary that a proper balance be maintained between the ink and moisture at all times. If the amount of ink or moisture, or the balance therebetween, is not maintained within predetermined ranges, noticeable copy degradation will result. For example, excessive moisture or an excessive moisture/ink ratio will reduce the ink transferred, resulting in copies with low optical density image areas. On the other hand, low moisture or excessive ink will cause the image areas to be blurred and may result in background toning.
In general terms, one of the primary problems over the years has been that the ink and moisture requirements for producing quality copies vary significantly with changes in operating and environmental conditions. For example, variations in temperature and humidity will change the amount of moisture required by the master for quality copies. Also, certain plates or masters, both referred to herein generally as "masters" such as those of the zinc oxide type, undergo changes during copy runs which have an effect upon the amount of moisture required. The moisture/ink requirements also may be affected by the presence of additional moisture introduced into the system as new masters are loaded in sequence for relatively short copy runs, wherein each new master is "wet" and adds moisture to the system.
One of the major problems of lithographic duplication has been to maintain proper ink/moisture balance during copy runs. Various controls and systems have been proposed or manufactured which have in some way monitored the ink and/or moisture conditions and provided means for adjusting the respective feed rates. Such controls have provided satisfactory results under many operating conditions, yet under some conditions, for one reason or another, have not maintained the ink/moisture balance within acceptable limits. This deficiency of conventional systems may be attributed at least in part to the fact that the ink and moisture controls were operated independently of each other while, in fact, the two conditions are closely interrelated as the ink and moisture become mixed or emulsified by way of the master cylinder. Thus, in order to provide improved ink/moisture balance for a very wide range of operating conditions, the interrelationship between the two systems should be taken into account. It would be desireable to have a control which supplies ink and moisture in a manner which recognizes this interrelationship and provides appropriate interface between the ink and moisture control circuits.
Therefore, it is an object of the present invention to provide a novel control system for a lithographic duplicator with means for interfacing the ink and moisture feed controls to provide improved ink/moisture balance over a wide range of operating conditions.
It is another object of the present invention to provide a unique ink/moisture control system with interfaced circuit means which effects changes in the moisture feed rate in response to corresponding changes in the ink feed rate to provide improved ink/moisture balance.
It is a further object of the present invention to provide a novel ink and moisture control system with interface circuit means which momentarily increases the moisture feed rate in response to the addition of ink to the duplicator system, whereby the proper ink/moisture balance is maintained particularly under high coverage conditions.
Still another object of the present invention is to provide a versatile control system which is responsive to various operating and environmental conditions to control the ink and moisture feed rates, and which includes means for interfacing the ink and moisture controls.